あ〜〜〜、感想というか、あきれてるんでしょ！

教えてgoo

http://oshiete.goo.ne.jp/qa/6064952.html

<!DOCTYPE html>
<title></title>
<body>

<script><!--

var Heikin = function () {
  var ary;

  this.reset = function () {
    ary = [ ];
  };
  
  this.push = function (n) {
    ary.push (n);
    return this.getCount();
  };
  
  this.getCount = function() {
    return ary.length
  };

  this.getAverage = function() {
    return eval (ary.join ('+')) / ary.length;
  };
}

//____________

var keisan = new Heikin;
var max = 5; //ここ15ね
var inp;
var cnt;

keisan.reset();
do {
  inp = window.prompt ('点数を入力してください。');
  cnt = keisan.push (inp);
}
while (cnt < max)

alert( "heikin =" + keisan.getAverage() );

//-->
</script>